Step function generator



May 21, 1963 R. D. JABLONSKY STEP FUNCTION GENERATOR Filed 001;. 24, 1960 I ll V3 "2 Brush Posxlzba Boy ,Uo/WD waoA/slfy;

INVENTOR BMQj QJ +11;

United States Patent 3,696,966 STEP FUNCTHUN GENERATQR Roy Donald Jahlonslry, Altadena, Calih, assignor to Giannini (Iontrols Corporation, Duarte, alif., a cor poration of New York Filed Oct. 24, 196i), Ser. No. MAS?) 4 Claims. (til. 323-43.5)

This invention has to do generally with developing a step voltage by movement of a brush assembly relative to a commutator.

When a brush of conventional form moves over two adjacent commutator segments at difierent potentials, it is difficult or impossible to prevent the brush from either leaving one segment before engaging the next, which momentarily opens the circuit; or maintaining contact with one segment after engaging the next, which shorts the two segments and typically produces an output voltage of intermediate value, or a half step.

A primary object of the invention is to avoid such disadvantages of previous commutator systems.

The invention accomplishes that and other objects by utilizing a plurality of longitudinally displaced brush elements, connected in parallel. A suitably oriented unidirectional conductive device is inserted in series with at least one of the brushes. The spacing and dimensions of the brush elements are subject to certain limitations, to be described.

A particular advantage of the invention is that each of the brush elements may have substantially any desired form.

Moreover, the novel brush arrangement of the invention does not interfere with normal operation of switching mechanism in the commutator circuits, as for the purpose of eliminating selected voltage steps, for example.

The invention is useful for producing a basic controllable step signal, which can readily be converted into digital pulses by circuitry of known type.

A full understanding of the invention, and of its further objects and advantages, will be had from the following description or" an illustrative manner of carrying it out, of which description the accompanying drawings form a part. Particulars of that description are intended only as illustration, and not as a limitation upon the scope of the invention, which is defined in the appended claims.

In the drawings:

FIG. 1 is a schematic drawing representing an illustrative embodiment of the invention;

FIG. 2 is a schematic drawing, corresponding to a portion of FIG. 1 at enlarged scale, and showing the parts in a different position; and

FIG. 3 is a graph illustrating an illustrative output step voltage in accordance with the invention.

In the drawing a commutator is indicated schematically at 10, with mutually spaced commutator segments C C C etc., to O The segments are separated by insulating material represented at 12, preferably providing a smooth contact or working surface 14 for brush engagement. The actual construction of the commutator may be conventional, a wide variety of such structures being well known.

Means of any desired type are provided for supplying to the commutator segments respective potentials forming a sequence of discrete values. As illustrated, the resistances R R etc., to R are connected in series with a source of direct current power represented as the battery 30, and act as a voltage divider. One terminal of the battery is connected to a source of reference potential, shown as the ground connection 32. The commutator segments are connected to the respective terminals and junctions of the resistance chain, as shown. If the resistance are all equal, for example, the potentials of the commutator segments then form a uniform series of N +1 values from zero to the voltage of source 30.

A brush assembly is indicated schematically at 20 and typically comprises two brush elements B and B mounted in insulated relation on a brush carrier 22. Carrier 22 is movable longitudinally of commutator 10, as indicated schematically by the arrow 24. Many suitable structures are well known for producing and controlling such movement. Resilient means of any siutable type, not explicitly shown, are preferably provided for maintaining the contact faces of brush elements B and B in effective engagement with working surface 14 of the commutator during that relative movement. For example, each brush element may comprise a block of conductive material transversely movable in a guiding bore in a carrier block of insulating material, and resiliently urged bodily toward commutator face '14. Alternatively, each brush may comprise a strip of resilient sheet metal having one end fixedly mounted on the brush carrier and having a surface adjacent the other end yieldingly engaging the commutator face. Many other suitable types of brush structure are well known.

The two brush elements B and B are connected in parallel to the output terminal 40 via the respective lines 42 and .4. Terminal 469 may be connected to any desired device for utilizing the voltage signal, suitable impedance isolating means being preferably provided if not contained inherently in the device. An illustrative utilization device is represented schematically at 50 as a load resistance R which is ordinarily high compared to the total resistance of R to R One end of R is connected to terminal 40 and the other end to a suitable reference potential at 52. That reference potential is typically at or beyond the potential value of one end of the commutator. The polarity of the commutator voltage may then be considered to be that of its other end relative to the reference potential. In the system illustrated, the reference potential is taken as ground, which is equal to the potential of the left hand end of commutator 10 as shown in \FIG. 1. The polarity of the commutator voltage is then that of its right hand end, which is illustratively shown as positive.

In accordance with one aspect of the present invention, certain relationships must be satisfied by the dimensions of the commutator and brush assembly. As illustrated in FIG. 2, the spacing between two typical adjacent commutator segments C and C is represented by S; the longitudinal dimension of each commutator segment is represented by D; the spacing between adjacent boundaries of the brush elements is represented by s; the longitudinal dimension of the contact surface of each brush element is represented by d; and the overall longitudinal dimension of both brush contact surfaces is represented by L, where L=s+2d. With that notation, the parts are so dimensioned and arranged that It is then impossible for one of the brush elements to short-circuit two adjacent commutator segments. Also lt is then impossible for the two brush elements to straddle a commutator segment with neither element contacting it. Finally L It is then impossible for both brush elements to be between two commutator segments in open circuit condition.

In accordance with a further aspect of the invention, unidirectional devices are connected in series with the respective brush elements B and B as indicated schematically at 46 and 48, respectively. Those devices are shown illustratively as semiconductor diodes, and will be referred to as diodes for convenience of description. However, many other types of devices are known that provide relatively low resistance for current flow in one direction and relatively high resistance for current flow in the reverse direction. Any such device having suitable properties may be utilized in the present system.

The polarity of both diodes 46 and 48 is the same and is such as to pass current of the polarity of the commutator, as already defined, from the brush assembly toward outlet terminal 40.

In operation of the described system, when only one commutator segment is engaged, whether by one brush element or by both, the potential of that segment is transmitted through one or both diodes to output terminal 4% and load R In FIG. 2, for example, the potential of segment C is transmitted via brush B brush B being ineffective.

When the two brush elements engage different segments, the effective output potential is that of the segment having the larger potential difference with respect to the reference potential at 52. In FIG. 1, for example, the effective potential is that of segment C Although segment C is contacted by brush B that contact is ineffective to lower the output potential, due to blocking action of diode 46. The higher potential transmitted from brush B via diode 4-8 may be considered to back bias diode 46, making brush element B ineffective.

Accordingly, as the brush assembly moves toward higher potentials relative to reference level 5 2., the potential at output terminal 40 increases in discrete steps in one-to-one correspondence to the commutator segments. Each step occurs at the moment that the leading edge 60 of the leading brush element B first contacts the commutator element. Such a series of potential steps is represented in FIG. 3.

As the brush assembly moves in the opposite direction, toward the reference potential, the output potential decreases correspondingly, each step down occurring at substantially the same brush position as the corresponding step up.

Since the diode in series with the brush on the high potential side is never reverse biased, it may be omitted if preferred. However, it is ordinarily advantageous to include both diodes in the circuit. The series resistance to terminal 40 is then more nearly independent of brush movement, since it includes the forward resistance of one diode or the other. When R is sufliciently high, that consideration becomes less significant. Hence, the invention includes within its scope use of only one unidirectional device.

If, for some reason, the commutator segments are relatively narrow compared to the spacing between them, it may be impossible to satisfy both conditions (2) and (3) at the same time with only two brush elements of suitable width. That is true, for example, if

That difficulty may be avoided by providing three or more suitably spaced brush elements, connected in parallel. A

diode or equivalent device is preferably connected in series with each brush element, or at least in series with each element except that at highest potential.

It will be seen that the described system permits deletion of a selected potential step, for example by shorting a selected one of the resistances R to R or by switching the connection of one of the commutator segments from its normal resistance junction to one of the adjacent junctions. In the first instance, all steps become slightly greater; in the second, the potential step deleted is added to an adjacent step, making the latter twice as large.

1 claim:

1. A system for producing an output potential that varies as a progressive step function with respect to a reference voltage, said system comprising the combination of commutator means comprising a plurality of sequentially arranged, mutually spaced commutator segments, means for supplying to the segments respective potentials having a selected polarity with respect to the reference voltage and increasing progressively in value in one direction, brush means movable relative to the commutator means to engage the segments sequentially, said brush means comprising a plurality of mutually spaced brush elements having respective contact surfaces, the longitudinal dimension of the surface of each element being insufiicient to bridge the space between adjacent segments in any position of the brush means, and the overall longitudinal dimension of the surfaces of all elements ,being sufiicient to bridge the space between adjacent segments, on output terminal connected to all the brush elements in parallel, and a unidirectional device connected in series with at least each of the brush elements of less than highest potential in such polarity as to pass current of said polarity toward the terminal.

2. A system as set forth in claim 1 and including a unidirectional device connected in said polarity in series with each brush element, all said unidirectional devices having substantially equal resistances in the forward direction.

3. A system as set forth in claim 1 and wherein the brush means comprises only two brush elements.

4. A system for producing an output potential that varies as a progressive step function with respect to a reference voltage, said system comprising the combination of commutator means comprising a plurality of sequentially arranged, mutually spaced commutator segments, means for supplying to the segments respective potentials having a selected polarity with respect to the reference voltage and increasing progressively in value in one direction, brush means movable relative to the commutator means to engage the segments sequentially, said brush means comprising a plurality of mutually spaced brush elements having respective contact surfaces, said surfaces being adapted to maintain continuous contact of at least one surface with at least one segment and to prevent simultaneous contact of any one surface with more than one segment, an output terminal connected to all the brush elements in parallel, and a unidirectional device connected in series with at least each of the brush elements of less than highest potential in such polarity as to pass current of said polarity toward the terminal.

References flirted in the file of this patent UNITED STATES PATENTS 2,231,607 Westendorp Feb. 11, 1941 

1. A SYSTEM FOR PRODUCING AN OUTPUT POTENTIAL THAT VARIES AS A PROGRESSIVE STEP FUNCTION WITH RESPECT TO A REFERENCE VOLTAGE, SAID SYSTEM COMPRISING THE COMBINATION OF COMMUTATOR MEANS COMPRISING A PLURALITY OF SEQUENTIAL ARRANGED, MUTUALLY SPACED COMMUTATOR SEGMENTS, MEANS FOR APPLYING TO THE SEGMENTS RESPECTIVE POTENTIALS HAVING A SELECTED POLARITY WITH RESPECT TO THE REFERENCE VOLTAGE AND INCREASING PROGRESSIVELY IN VALUE IN ONE DIRECTION, BRUSH MEANS MOVABLE RELATIVE TO THE COMMUTATOR MEANS TO ENGAGE THE SEGMENTS SEQUENTIALLY, SAID BRUSH MEANS COMPRISING A PLURALITY OF MUTUALLY SPACED BRUSH ELEMENTS HAVING RESPECTIVE CONTACT SURFACES, THE LONGITUDINAL DIMENSION OF THE SURFACE OF EACH ELEMENT BEING INSUFFICIENT TO BRIDGE THE SPACE BETWEEN ADJACENT SEGMENTS IN ANY POSITION OF THE BRUSH MEANS, AND THE OVERALL LONGITUDINAL DIMENSION OF THE SURFACES OF ALL ELEMENTS BEING SUFFICIENT TO BRIDGE THE SPACE BETWEEN ADJACENT SEGMENTS, AN OUTPUT TERMINAL CONNECTED TO ALL THE BRUSH ELEMENTS IN PARALLEL, AND A UNDIRECTIONAL DEVICE CONNECTED IN SERIES WITH AT LEAST EACH OF THE BRUSH ELEMENTS OF LESS THAN HIGHEST POTENTIAL IN SUCH POLARITY AS TO PASS CURRENT OF SAID POLARITY TOWARD THE TERMINAL. 